<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>
<script type="text/javascript">
	
	var a = [1,2,3];
	var b = a;
	b = null;
	alert(a);//[1,2,3]

	var a = [1,2,3]; //FX000021370 = [1,2,3]
	var b = [a];
	a = null;
	alert(b);//[[1,2,3]]


</script>
</body>
</html>